U.S. patent number 4,556,845 [Application Number 06/378,697] was granted by the patent office on 1985-12-03 for method for monitoring deposition rate using an eddy current detector.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Douglas H. Strope, Thomas E. Wray.
United States Patent |
4,556,845 |
Strope , et al. |
December 3, 1985 |
Method for monitoring deposition rate using an eddy current
detector
Abstract
A conductive film deposition rate monitoring method for
measuring the real time deposition rate of a metallic deposition
process particularly an electroless plating bath, including the
steps of positioning an eddy current detector within a
predetermined distance of a test surface where the deposition is to
be deposited, and the step of monitoring the output of the
detector. The apparatus comprises an eddy current sensor and a
non-metallic housing for the sensor, having a non-conductive wall
of predetermined thickness between the sensor and the surface of
the wall distant from the sensor, the distant wall being immersed
in the deposition environment, such as a plating bath, so that a
deposit takes place on the distant surface, and measuring means
connected to the output of the sensor for measuring the amplitude
and rate of change of the output of the sensor.
Inventors: |
Strope; Douglas H. (Apalachin,
NY), Wray; Thomas E. (Vestal, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
23494185 |
Appl.
No.: |
06/378,697 |
Filed: |
May 17, 1982 |
Current U.S.
Class: |
324/230;
427/10 |
Current CPC
Class: |
G01B
7/105 (20130101) |
Current International
Class: |
G01N
27/72 (20060101); G01B 7/06 (20060101); G01B
7/02 (20060101); G01R 33/12 (20060101); G01B
007/10 (); G01R 033/12 () |
Field of
Search: |
;324/229,230,231
;427/8,9,10 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Canestaro, "Continuous Monitoring of Plating Bath Plating Rate",
IBM Tech. Disclosure Bul. vol. 17, No. 6, pp. 1581-1582,
11/1974..
|
Primary Examiner: Strecker; Gerard R.
Assistant Examiner: Snow; Walter E.
Attorney, Agent or Firm: Smith; Marilyn D. Galbi; Elmer W.
Jancin, Jr.; J.
Claims
We claim:
1. The method of measuring the rate of initiation of a plating
operation in an electroless plating bath by the steps of:
positioning an eddy current detector at a predetermined distance of
a test surface where electroless plating is taking place;
monitoring the output of the eddy current detector; and
determining the rate of change of said output during the initiation
phase of said plating operation whereby said rate of change is
indicative of the rate of initiation of said plating operation.
2. The method of determining the seeding effectiveness of an
electroless plating bath by the steps of:
positioning the eddy current detector at a predetermined distance
of a test surface where deposition is taking place;
immersing said eddy current detector and said test surface in said
plating bath; and
measuring the time from the immersion of the probe to the
initiation of plating whereby said time is indicative of the
seeding effectiveness of said electroless plating bath.
3. An improved method for monitoring the thickness of deposition in
a metallic deposition environment comprising the steps of:
positioning an eddy current detector at a predetermined distance of
a test surface in a wet electroless plating bath where the
deposition is taking place;
measuring the output of the eddy current detector from the time of
the immersion of the probe in the wet electroless plating bath to
the time when plating commences whereby said time is indicative of
the seeding effectiveness of said electroless plating bath; and
measuring the output of the eddy current detector during the
initiation of the plating operation.
4. A method of monitoring the real time deposition rate of a
metallic deposition process by the steps of:
utilizing an eddy current sensor;
connecting measuring means to the output of the eddy current
sensor;
positioning the eddy current sensor at a predetermined distance of
a test surface in a wet electroless plating bath where the
deposition is taking place;
monitoring the output of the sensor with respect to the amplitude
and the rate of change of the output;
recording the output curve of the sensor;
determining the seeding effectiveness and the plating bath solution
activity from the initial portion of the output curve which
indicates the time from the immersion of the sensor to a time when
plating commences;
determining the initiation of the plating operation from the steep
portion of the curve;
determining the thickness of the plating after a plating operation
has taken place from the central portion of the curve; and
determining displacement measurements from the final portion of the
curve.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates generally to conductive film deposition rate
monitors and more particularly to a method and apparatus for
monitoring the deposition rate and thickness of deposition in a
metallic deposition environment, particularly in an electroless
(non-electrolytic) plating bath.
(2) Description of the Prior Art
Plating thickness measuring devices are known in the art. Such
devices are usually employed to determine the thickness of a
plating after it has been deposited, i.e., as a post-plating
measurement. Also the use of eddy current devices to measure
metallic deposition thickness is well known. In electroless
plating, there are many varying factors which determine the degree
of success to be achieved in the plating operation. One important
factor is the rate of plating.
SUMMARY OF THE INVENTION
The present invention provides a deposition rate monitoring method
and apparatus which measure the real time deposition rate of a
metallic deposition process, particularly an electroless plating
bath, including the step of positioning an eddy current detector
within a predetermined distance of a test surface where the
deposition is to be deposited and the step of monitoring the output
of the detector. The apparatus comprises an eddy current sensor and
a non-metallic housing or cap for the sensor, having a
non-conductive wall of predetermined thickness between the sensor
and the surface of the wall distant from the sensor, the distant
wall being immersed in the deposition environment, such as a
plating bath, so that a deposit takes place on the distant surface,
and measuring means connected to the output of the sensor for
measuring the amplitude and rate of change of the output of the
sensor.
With respect to electroless plating, this invention will provide
method and means to test seeding processes and plating
initiation.
It is accordingly an object of this invention to provide an
improved deposition rate monitoring method and apparatus,
particularly suited for electroless plating.
Another object of the invention is to provide an improved plating
rate monitor which operates in real time and in the bath
itself.
A further object of the invention is to provide an improved plating
rate monitor which operates in real time on a continuing basis.
Another object of the invention is to provide improved method and
means for testing seeding processes and plating initiation.
The foregoing and other objects features and advantages of the
invention will be apparent from the following more particular
description of a preferred embodiment of the invention, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic drawing of a deposition rate monitoring
apparatus in accordance with the preferred embodiment of the
invention.
FIG. 2 is a detailed cross sectional view of a plastic end cap as
employed in the arrangement shown in FIG. 1.
FIG. 3 is a graph illustrating the operation of the embodiment
shown in FIG. 1.
FIG. 4 shows a deposition rate monitor in a vacuum deposition
environment.
Similar reference characters refer to similar parts in each of the
several views.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In carrying out the method of conductive plating monitoring
according to this invention, an eddy current detector is positioned
at a predetermined distance from a surface on which metallic
deposition can take place. The assembly is placed in the deposition
environment and the output of the detector is monitored with
respect to the amplitude and the rate of change of the output,
thereby indicating the thickness of the deposition and the rate at
which it is being deposited.
A preferred arrangement of apparatus for electroless plating is
shown in FIG. 1 of the drawings, in which a plating bath 3
comprises a plating liquid body 5 enclosed in a suitable container,
a portion of which container wall is shown at 7. By means of a
bracket 9 or other suspension device an eddy current sensing probe
11 is suspended at a suitable distance beneath the surface of the
plating bath, for example, of the order of six inches. A liquid
proof housing is provided for the sensing element including a cap
13, the details of which will be subsequently explained, and a
liquid-proof connecting cable 15 is provided, which also acts as a
suspension for the sensor. The output leads from the sensor are
supplied to the input of a detector driver unit 17, which will
produce an output signal which will have an amplitude and rate of
change that is dependent upon the thickness and rate at which a
metallic deposit is deposited onto the cap 13.
The details of the eddy current sensor unit 11 and the associated
detector driver unit 17 are not shown, since they may take any
number of forms well known in the art. One such type of eddy
current sensor device is manufactured by the Bently-Nevada
Corporation, and is a regular commercially available item.
The output of the detector driver unit 17 is supplied, for example,
to the input of a conventional strip chart recorder 19 and may also
be supplied, via an analog to digital converter 21, to the input of
a microcomputer 23, the output of which is in turn connected to an
output device 25, which may be, for example, a visual display, a
recording device, or an output printer.
Referring to FIG. 2 of the drawings, the eddy current probe or
sensor 11 comprises a body element of non-conductive material
enclosing a coil which when energized will produce eddy currents in
any metallic surface nearby, the effect of the eddy currents being
determined by the detector driver unit 17 of FIG. 1. The sensor 11
is threaded for all or a greater portion of its length and is
provided with a cap 13 of non-magnetic, non-conductive material
having an internal thread which corresponds to the threads on the
sensor 11. The lower wall of the cap 13 has a predetermined
thickness designated by d of known and accurately measured amount.
The cap 13 is screwed onto to the sensor 11, and the assembly is
rendered liquid proof by any suitable means, such as a rubber
enclosure or other arrangement to protect the assembly from liquid
except for the lower wall. When immersed in the plating path, after
appropriate seeding, a plating deposit will take place on the outer
portion of the lower wall, and this metallic deposit will be
detected by the eddy current sensor, to provide an indication not
only of the thickness of the plating but the rate at which it is
occurring as shown on the strip chart recorder 19 or determined by
the microcomputer 23.
FIG. 3 is a dimensionless graph showing the relationship between
time, starting with the immersion of the sensor, and the eddy
current loss as measured by the sensing device. The initial portion
of the curve, designated as "seeding effectiveness," indicates the
time from the immersion of the probe to the time, at 15, when
plating commences. This time appears to be an indicator of (1)
seeding effectiveness (using different methods), and (2) plating
bath solution activity (varying chemical parameters). Suitable
characterization or standardization of either of these factors will
enable study of the variation of the other factor. The portion of
the curve which rises from 15 to a peak value at 17, is the segment
used for measurement of initiation of the plating operation. It can
be seen that a high resolution is obtained with this curve and the
rate, of course, is proportional to the slope of the curve. The
central portion of the curve is the section which is used for
thickness measurement of coatings after a plating operation has
taken place, while the very right hand portion with substantially
zero slope is commonly used for displacement measurements with eddy
current sensors by using thick conductive targets and a varying
airgap.
FIG. 4 shows the use of the invention with a conventional vacuum
deposition system. A vacuum chamber 19 contains a source 21 of
metallic vapor or particles, which are directed to an object 23 on
which a metal layer is to be deposited. The sensor 11, 13 is
inserted in the chamber as shown, and metal is also deposited on
the sensor. The remainder of the apparatus, its operation and
characteristics are similar to those described above.
From the foregoing it will be apparent that the present invention
provides an improved method and apparatus for determining the
thickness of plating being provided in an electroless plating bath
as well as the rate of deposition.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *